1. Field of the Invention
The present invention relates to a cassette for containing a liquid crystal display (LCD) device, and more particularly, to a cassette for an LCD device capable of preventing defects of the LCD device generated when an active region of a substrate contacts a supporting bar.
2. Discussion of the Background Art
Recently, various portable electric devices, such as mobile phones, personal digital assistant (PDA), and notebook computers have been developed having small sizes, light weights, and power-efficient operations. Accordingly, flat panel display devices, such as liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), and vacuum fluorescent displays (VFDs), have been developed. Of these flat panel display devices, LCDs are currently mass-produced because of their simple driving scheme and superior image quality.
FIG. 1 is a cross sectional view of an LCD device according to the related art. As shown in FIG. 1, an LCD device 1 includes a lower substrate 5, an upper substrate 3, and a liquid crystal layer 7 formed therebetween. The lower substrate 5 is a switching device array substrate, and includes a plurality of pixels (not shown) and a switching device, such as a thin film transistor (TFT), formed on each pixel. The upper substrate 3 is a color filter substrate and includes a color filter layer for displaying colors. In addition, a pixel electrode and a common electrode are formed on the lower substrate 5 and the upper substrate 3, respectively. An alignment layer is formed on both the lower and upper substrates 5 and 3 to align liquid crystal molecules of the liquid crystal layer 7.
The lower substrate 5 and the upper substrate 3 are attached along a perimeter by a sealing material 9, and a liquid crystal layer 7 is confined within the perimeter. In addition, orientation of the liquid crystal molecules of the liquid crystal layer 7 is controlled through the switching device formed on the lower substrate 5 to control amounts of light transmitted through the liquid crystal layer 7 to display an image.
FIG. 2 is a flow chart of a fabrication method for an LCD device according to the related art. As shown in FIG. 2, a fabrication method includes three sub-processes for manufacturing an LCD device: a switching device array substrate process for forming the driving device on the lower substrate 5; a color filter substrate process for forming the color filter on the upper substrate 3; and a cell forming process.
In Step S101, a plurality of gate lines and data lines are formed on the lower substrate 5 to define a pixel area in the switching device array process, and the thin film transistor connected to both the gate line and the data line is formed on the each pixel area. In addition, a pixel electrode connected to the thin film transistor to drive the liquid crystal layer according to a signal applied through the thin film transistor, is formed by the switching device array process.
In Step S104, R, G, and B color filter layers for reproducing the color and a common electrode are formed on the upper substrate 3 by the color filter process.
In Step S102 and S105, alignment layers are formed on the lower substrate 5 and the upper substrate 3. Then, the alignment layers are individually rubbed to induce surface anchoring (i.e. a pretilt angle and alignment direction) for the liquid crystal molecules of the liquid crystal layer 7. In Step S103, spacers are dispersed onto the lower substrate 5 for maintaining a uniform cell gap between the lower and upper substrates 5 and 3. In Step S106, a sealing material is formed along outer portions of the upper substrate 3. In Step S107, the lower and upper substrates 5 and 3 pressed together to be bond the substrates 5 and 3.
The lower substrate 5 and the upper substrate 3 are both made from a glass substrate that includes a plurality of unit panel areas on which the switching devices and the color filter layer are formed. In Step S108, the bonded upper and lower glass substrates 5 and 3 are cut into unit panels. In Step S109, liquid crystal material is injected into the gap formed between the upper and lower substrates 5 and 3 of the unit panels through a liquid crystal injection hole. In Step S109, the filled unit panel is completed by sealing the liquid crystal injection hole. In Step S110, the filled and sealed unit panel is tested.
The above steps are each performed on respective processing lines. Accordingly, the substrates 3 and 5 that have undergone one process are transferred to a subsequent processing line by a conveyor or an auto guide vehicle. However, when an LCD device having a large area is being fabricated, a large substrate has to be transferred in a factory. Since conveyors are not well suited for transferring the large substrate, the auto guide vehicle is mainly used to transfer the large substrate to a processing line.
When using the auto guide vehicle, a plurality of substrates is received in a cassette thereby to be transferred. Unloading the substrate from a processing line, receiving the substrate in a cassette, and loading the received cassette onto a next processing line are performed by a robot.
FIG. 3 shows a cassette for an LCD device according to the related art in which substrates are received for transfer by an auto guide vehicle. As shown, the cassette 40 of the related art for receiving an LCD device comprises a main body 41, a supporting bar 42 formed in the body to receive a substrate 10, and a pad 44 formed at the supporting bar 42 to fix the substrate 10 by contacting the substrate 10. The supporting bars 42 are formed in the body 41 as a multiple layers thereby to receive a plurality of liquid crystal panels 3.
FIG. 4 is a plan view showing the interior of the cassette 40 of FIG. 3 in accordance with the related art, in which the substrate 10 is received on one layer in the cassette 40. As shown, a plurality of LCD panels 3 are formed on the substrate 10, and the LCD panels 3 are separated from each other with a certain distance by a dummy region. A plurality of supporting bars 42 for supporting the substrate 10 are formed in the body 41 (the same number of supporting bars 42 are formed at upper and lower portions of the body 41). That is, the substrate 10 is received in the cassette 40 by the plural supporting bars 42. The supporting bar 42 is provided with a plurality of pads 44. The pads 44 are formed of a material such as rubber able to absorb an impact and having an excellent coefficient of friction for fixing the substrate 10 and to prevent impact damage to the substrate 10. The pad 44 contacts the dummy region 4 of the substrate 10.
When the substrate 10 is received in the cassette 40, the cassette 40 is transferred to a next processing line by an auto guide vehicle and then unloaded from the cassette 40 by a robot or other means thereby to undergo a corresponding process.
However, the cassette of the related for an LCD device has the following problems.
As techniques for fabricating LCD device develop and the number of electronic devices employing LCD devices increases, LCD devices having various sizes are being fabricated. Methods for fabricating LCD devices having various sizes in one fabrication line are widely used. Accordingly, the size of an LCD panel formed on a substrate to be transferred from one processing line to another processing line is not always the same, but varies according to a model of a LCD device being fabricated.
FIG. 5 is a view showing a cassette 40 in which a substrate 10 has been received on which LCD panels 30 are formed each having a wider area than that of the LCD panels of FIG. 4. Since the LCD Panels shown in FIGS. 4 and 5 have different sizes from each other, a position on the substrate 10 where the LCD panel 3 is formed in FIG. 5 is different from a position of the LCD panel 3 on the substrate 10 in FIG. 4. A pad 44 is positioned at a dummy region 4 of the substrate 10 in FIG. 4. However, in FIG. 5, the pad 44 is positioned differently relative to the LCD panels 3.
When the substrate 10 is received in the cassette 40 of FIG. 4, a dummy region of the substrate 10 contacts the pad 4. As a result, even when the substrate 10 pressed, a defect is not generated. However, when the pad 4 is positioned within the LCD panel 3 as shown in FIG. 5, if the substrate 10 is pressed, the pad 44 presses on an area of the LCD panel 3 for displaying an image and a defect in the LCD device may result. The above problem occurs primarily at the time of transferring attached LCD panels that have been received in the cassette 40 to another processing line. As the LCD panel 3 is pressed against a pad, a stain is generated on the LCD device.